Investigation of the structure of a stabilized reaction intermediate formed during the catalytic conversion of selected aldehydes to their corresponding acids by aldehyde dehydrogenase is proposed. This work will focus on a complex formed at pH 5.3 with aldehyde dehydrogenase isolated from Saccharomyces cerevisiae (Baker's yeast) (ALDH), nicotinamide adenine dinucleotide (NAD+), and either 4-(dimethlyamino)benzaldehyde (DABA) or 4-(dimethylamino)cinnamaldehyde (DACA). The solution pH and concentration ratio for optimum formation and stability of the complex will be determined. The structure of the modified aldehyde molecule, when trapped within the dehydrogenase as part of the complex, will be probed using resonance Raman pectroscopy. In order to help stabilize the complex, spectroscopic data will be collected with the complex maintained at liquid nitrogen temperature (77 K) in a cell to be constructed. The structural information obtained will be used to test a mechanism proposed for the formation of such complexes during aldehyde dehydrogenase catalysis. The generally accepted catalytic mechanism for aldehyde dehydrogenases will be discussed in light of this new information. The long-term objective of this research plan is to develop a better understanding of the catalytic mechanism of aldehyde dehydrogenase. This information is essential in order to develop new and improved medicinal agents for the treatment of alcohol abuse and alcoholism. The specific aims include: 1) determination of conditions for increased formation and stability of the ALDH/NAD+/DABA (DACA) complex; 2) collection and analysis of cryo-resonance Raman spectra of the chromophoric aldehyde probe as modified during the formation of the complex; 3) refinement of a mechanism proposed for the formation of the complex based on the observed spectroscopic data.